How do you calculate head?

[Rangeball]

This is something I need to get a handle on.

I have a 21,200 gallon 16'x30' IG vinyl pool. A skimmer, main drain in the center of the 8' deep end, and one return. Pump is currently an AG Pentair Dynamo 1hp (long story).

The pump sits on the deck about 1' above the water surface and 6' from the pool. I estimate the skimmer piping runs 15' about 1.5' under the water surface, then up 2' and over 2' to the pump. Main drain runs 10' 8' under the water surface, then up 10' then over 2' to the pump. Return runs down 4' then 36' 1' under the water surface to the pool.

Any guesses? Please educate me on how this is calculated. I'm trying to get a precise idea on my GPM flow, but the chart is curved and based on "total head".

Thanks

[mshumack]

I printed a couple of pages off the web with very detailed instructions on calaculating head both on a working system (with pressure and vacuum gages) and for new construction (pipe size, lenght of runs, number of fittings, etc.) It was pretty invloved. Unfortunately, now I can't find it. I'll look some more when I get a chance tomorrow. For now, you can start with this page http://www.poolplaza.com/pump-head.shtml
Good luck
Mike

[mas985]

The easiest way is to assume 45-65 feet of head.

The most accurate way is to measured it:

Total head = Return Head + Suction Head

Return Head = 2.31 * Filter PSI
Suction Head = 1.13 * Pump Vacuum (inches mercury)

If you do not want to purchase a vacuum guage then you can assume that suction head is about 40% of the return head (only works for no solar or extra return features) so

Total head ~ 3.2 * Filter PSI

The hardest way and probably least accurate is to use the plumbing configuration. Problem with this is not all PVC pipe is the same friction coeficients and it is difficult to find friction factors for every plumbing element.

[GraceByDesign]

Oh, great. Not only do we need a chem major to understand all this pool stuff, now we need advanced math degrees, too!

Grace

Avid reader of this forum
but no pool... yet!

[Rangeball]

Oh, great. Not only do we need a chem major to understand all this pool stuff, now we need advanced math degrees, too!

Grace

Avid reader of this forum
but no pool... yet!

Really.

I'm almost sorry I asked

[Rangeball]

Mike, Thanks for the link. I'll give it a look.

If you do not want to purchase a vacuum guage then you can assume that suction head is about 40% of the return head (only works for no solar or extra return features) so

Total head ~ 3.2 * Filter PSI

Thanks for the info.

By filter PSI I assume you mean what my filter gauge reads? Normal operation is 10 psi. So 3.2 x 10 psi = 32 head?

And right now my filter psi is 14 (lot's of cottonwood lately), so head has increased to 44.8?

Is that right?

[mas985]

Without a vacuum measurement, that is about a close as you will get. 32 is pretty low for head. Must be large pipes and a weak pump. Do you have a head curve for that pump? Just curious why the GPM is for that head.

[duraleigh]

Mark, Rangeball,

Yeah, my normal psi is 11....so 35tdh for my pool as well. I have a full-rated 1.5hp starite max-e pro, 2" suction pipe, and 2 - 1.5" return pipe.

I have always assumed mine (tdh) is low because my sand filter is so large....140gpm rating (950 lbs of sand)

That tdh on my pump curve works out to right at 100gpm.

[tenax]

holy crap! that is a big filter you have there...i can't even picture it! great beer keg!

[Rangeball]

Without a vacuum measurement, that is about a close as you will get. 32 is pretty low for head. Must be large pipes and a weak pump. Do you have a head curve for that pump? Just curious why the GPM is for that head.

Here's the data sheet and head curve PDF for my pump-

http://www.pentairpool.com/misc/pdfs...ynamo_pump.pdf

It's a 1 hp motor. It's also for an AG pool, and I have an IG. This is the pump that came with the pool when we bought the house, and when it burned out 4 years ago this is the same pump the pool store replaced it with (long before I started paying attention and asking questions ).

All my piping is 1.5". I'm trying to calculate GPM, which is why I needed to know the head

I have been thinking of a 3/4 HP whisperflow, but as long as this one is working, I don't need to spend the money.